Indoor during the week before work due to time of day and safety. Outdoors on the weekends weather permitting, and for all VO2 workouts because I feel like I am suffocating indoors on those efforts.
A couple of my more specific criteria:
- Most long endurance rides now that I have lots of time.
- VO2max intervals, hill repeats
- Skill sessions
- Most short duration PDC testing
- Endurance rides in the offseason, when it’s cold, or just sometimes when I don’t feel like fully kitting up etc.
- Longer intervals, 8+ min, threshold, SST, and over/unders.
- Some anaerobic interval repeats where I really want to bury myself sitting.
- Recovery rides - I kinda like chasing D. Diesel around Watopia to keep these really easy.
- Long duration PDC testing.
Tabata or short-short work I can do either way.
Doing the testing in the same modality that I ride the intervals helps mitigate the FTP/effort differences between outdoors and the trainer. So if my 20-60 minute test efforts are from the trainer, I feel pretty good doing my 2x20s on the trainer.
Otherwise, I don’t like riding in the rain - doesn’t happen much here, but with my trainer I will generally avoid it.
The last thing is safety… trainer is obviously much safer, and so sometimes I’ll default to that rather than risking life and limb with the crazies.